The present invention relates to a display and a method of driving the display and more particularly to a TFT (Thin Film Transistor) active matrix display.
For digitizing contents that have conventionally been provided in the form of paper, such as books and newspapers, a display with as high a resolution as printed matters is desired. The resolution of the currently available displays, however, is 200 ppi (pixels per inch) at the highest, far less than that of printed matters. The conventional displays have another problem that even at a resolution of around 200 ppi a large number of pixels used consumes a large amount of electricity.
A most effective method for reducing power consumption is to reduce a frame frequency. A reduction in frame frequency may be achieved by having a memory in pixels. In liquid crystal displays having a memory in pixels, an example of a conventional pixel circuit configuration related to this invention is disclosed in JP-A-2-272521.
In a system having a memory in pixels, JP-A-2003-302936 describes that, in an amorphous TFT, a transistor for driving an OLED (Organic Light Emitting Diode), an increased component of a threshold voltage (Vth) is removed by turning on or off a gate voltage and a drain voltage simultaneously.
Further, in the system having a memory in pixels, JP-A-2002-341828 describes that a display pixel circuit using organic EL (electroluminescence) devices adjusts a brightness of displayed image practically without reducing the number of grayscale levels of the image.
In such system having a memory in pixels, JP-A-10-319909 describes that a plurality of organic EL elements emit light for respective picture sub-frames with its own brightness, that images for each of sub-frames are visually combined and that brightness within a frame can be represented.
Further, in the system with a memory in pixels, JP-A-7-111341 describes that an organic thin film EL display reduces a failure rate caused by wire breaks and short circuits, by reducing a total wiring length and the number of crossings.
For a superfine resolution as high as printed matter, the number of pixels per unit area needs to be increased compared with the conventional displays. However, the use of the conventional display driving method to perform an image display at the superfine resolution requires increasing a reference clock frequency significantly, which results in a substantial increase in power consumption, making this method impractical.
One conceivable method for realizing a high resolution at low power consumption involves incorporating a memory in pixels and reducing the frame frequency. If a complex memory circuit such as static RAM or a CMOS transistor memory circuit is used, it is difficult to realize a high resolution.
To realize both a high resolution and a low power consumption at the same time, this invention adopts a memory-incorporated pixel system of single channel transistor configuration which is the simplest configuration. The memory-incorporated pixel system using the single channel transistor configuration has two single channel transistors for each pixel.
In the case of the CMOS transistor configuration, one of two reference voltage lines can be chosen, whereas the conventional single channel transistor configuration has only one reference voltage line and thus no method is available so far to switch from one state to another without adversely affecting the image display performance.
It is therefore an object of this invention to realize a display using a memory-incorporated pixel system of single channel transistor configuration which performs refreshing of image signal memories and updating of an image without adversely affecting the display performance and which has an ultrahigh resolution comparable to that of printed matter and a lower power consumption. It is also an object of this invention to provide a method of driving such a display.